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Saturday, October 31, 2020

Manage KVM Virtual Machines With Virsh Program

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Virsh, short for Virtual Shell, is a command line user interface for managing virtual guest machines. Virsh allows you to create, list, edit, start, restart, stop, suspend, resume, shutdown and delete VMs. It currently supports KVM, LXC, Xen, QEMU, OpenVZ, VirtualBox and VMware ESX. In this guide, we will be discussing how to manage KVM virtual machines with Virsh management user interface in Linux.

Make sure you have installed KVM and Virsh utility on your Linux machine. The following guides explains how to install KVM on DEB and RPM-based systems.

Manage KVM Virtual Machines With Virsh Commands

Getting help

If you are new to or don’t know how to work with Virsh interactive terminal, enter the following command to view the list of available commands along with brief description.

$ virsh help

You will see an extensive list of available virsh commands to manage KVM virtual machines from command line.

Display virsh commands help section

You don’t have to memorize everything. Just read the description of a command that you want to run and use it.

The commands are grouped into the following sections:

  • Domain Management,
  • Domain Monitoring,
  • Host and Hypervisor,
  • Checkpoint,
  • Interface,
  • Network Filter,
  • Networking,
  • Node Device,
  • Secret,
  • Snapshot,
  • Backup,
  • Storage Pool,
  • Storage Volume,
  • Virsh itself.

Each section contains the commands related to do particular set of tasks. You can view help section of a group, for example Networking, like below:

$ virsh help Networking

You will see commands related to do networking tasks:

 Networking (help keyword 'network'):
    net-autostart                  autostart a network
    net-create                     create a network from an XML file
    net-define                     define an inactive persistent virtual network or modify an existing persistent one from an XML file
    net-destroy                    destroy (stop) a network
    net-dhcp-leases                print lease info for a given network
    net-dumpxml                    network information in XML
    net-edit                       edit XML configuration for a network
    net-event                      Network Events
    net-info                       network information
    net-list                       list networks
    net-name                       convert a network UUID to network name
    net-start                      start a (previously defined) inactive network
    net-undefine                   undefine a persistent network
    net-update                     update parts of an existing network's configuration
    net-uuid                       convert a network name to network UUID
    net-port-list                  list network ports
    net-port-create                create a network port from an XML file
    net-port-dumpxml               network port information in XML
    net-port-delete                delete the specified network port

You can further display help section of a specific command as well. For example, I am going to display the help section of “net-name” command:

$ virsh help net-name
  NAME
    net-name - convert a network UUID to network name

  SYNOPSIS
    net-name <network>

  OPTIONS
    [--network] <string>  network uuid

List virtual machines

To view list of guest virtual machines in run or suspend mode, execute the following command:

$ virsh list
Id Name State
--------------------

As you can see, there are no guests in run or suspend mode.

You can use the –inactive option to list inactive guests.

To view all guest machines, run:

$ virsh list --all
 Id   Name            State
--------------------------------
 -    centos8-uefi    shut off
 -    nginx_centos8   shut off

As you see in the above output, I have two virtual machines namely “centos8-uefi” and “nginx_centos8”. Both are powered off.

Start Virtual machines

To start a virtual machine, for example “centos8-uefi”, run:

$ virsh start centos8-uefi

You will see an output like below:

Domain centos8-uefi started

To verify if the VM is running, use “list” command:

$ virsh list
 Id   Name           State
------------------------------
 1    centos8-uefi   running

Save Virtual machines

To save the current state of a running VM, run:

$ virsh save centos8-uefi centos8-save

Domain centos8-uefi saved to centos8-save

This command stops the guest named “centos8-uefi” and saves the data to a file called “centos8-save”. This will take a few moments depending upon the amount of memory in use by your guest machine.

Restore Virtual machines

To restore the previously saved state of a VM, just specify the file name like below:

$ virsh restore centos8-save 
Domain restored from centos8-save

Verify if the VM is restored using “list” command:

$ virsh list
 Id   Name           State
------------------------------
 4    centos8-uefi   running

Restart Virtual machines

To restart a running VM, run:

$ virsh reboot centos8-uefi
Domain centos8-uefi is being rebooted

Suspend/Pause Virtual machines

To suspend a running VM, do:

$ virsh suspend centos8-uefi 
Domain centos8-uefi suspended

Verify it with “list” command:

$ virsh list
 Id   Name           State
-----------------------------
 1    centos8-uefi   paused

Resume Virtual machines

To resume the paused VM, run:

$ virsh resume centos8-uefi 
Domain centos8-uefi resumed

Stop active Virtual machines

To forcibly stop an active VM, and leave it in the inactive state, run:

$ virsh destroy centos8-uefi
Domain centos8-uefi destroyed

You can also gracefully stop the VM instead of forcing it like below:

$ virsh destroy centos8-uefi --graceful
Domain centos8-uefi destroyed

Shutdown Virtual machines

To power off a running VM, do:

$ virsh shutdown centos8-uefi
Domain centos8-uefi is being shutdown

Retrieve Virtual machines XML dump

To display the XML configuration file of a VM in the standard output, run:

$ virsh dumpxml centos8-uefi

This command will display the complete configuration details (software and hardware) of the virtual machine:

Display Virtual machines XML configuration file

Display Virtual machines XML configuration file

You can also export the XML dump to a file instead of just displaying it in the standard output like below:

$ virsh dumpxml centos8-uefi > centos8.xml

This command will dump the “centos8-uefi” XML file in a file named “centos8.xml” and save it in the current working directory.

Create Virtual machines with XML dump

You can create a new virtual guest machine using the existing XML from previously created guests. First, create a XML dump as shown above and then create a new VM using the XML file like below:

$ virsh create centos8.xml 
Domain centos8-uefi created from centos8.xml

This command will create a new VM and start it immediately. You can verify it using command:

Create Virtual machines with XML dump

Create Virtual machines with XML dump

Edit Virtual machines XML configuration file

If you wanted to make any changes in a guest machines, you can simply edit its configuration file and do the changes as you wish. The guests can be edited either while they run or while they are offline.

$ virsh edit centos8-uefi

This command will open the file in your default editor that you set with $EDITOR variable.

Enable console access for Virtual machines

After creating KVM guest machines, you can access them via SSH, VNC client, Virt-viewer, Virt-manager and Cockpit web console etc. However, you can’t access them using “virsh console” command. The console command is used to connect the virtual serial console for the guest. To access KVM guests using “virsh console” command, you need to enable serial console access in the guest machine. Refer the following guide to enable virsh console access:

Rename Virtual machines

If you ever wanted to rename a virtual machine, refer the following guide.

Display Domain ID of Virtual machines

To find the domain id of a running guest virtual machine, run:

$ virsh domid centos8-uefi
2

Please note that the guest should be running to get its domain id.

Display Domain name of Virtual machines

To get the domain name of a running VM, run:

$ virsh domname <domain-id or domain-uuid>

Example:

$ virsh domname 2
centos8-uefi

Here, 2 is the domain id.

Display UUID of Virtual machines

To find the guest machine UUID, run:

$ virsh domuuid <domain-name or domain-id>

Example:

$ virsh domuuid centos8-uefi

Or,

$  virsh domuuid 2

Sample output:

de4100c4-632e-4c09-8dcf-bbde29170268

Display Virtual machines details

To display a guest machine’s information, use domain name, domain id or domain uuid like below:

$ virsh dominfo centos8-uefi

Or,

$ virsh dominfo 2

Or,

$ virsh dominfo de4100c4-632e-4c09-8dcf-bbde29170268

Sample output:

Id:             -
Name:           centos8-uefi
UUID:           de4100c4-632e-4c09-8dcf-bbde29170268
OS Type:        hvm
State:          shut off
CPU(s):         2
Max memory:     2097152 KiB
Used memory:    2097152 KiB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: apparmor
Security DOI:   0
Display Virtual machines details
Display Virtual machines details

Display host information

To get the information of your host system, run:

$ virsh nodeinfo

Sample output:

CPU model:           x86_64
CPU(s):              4
CPU frequency:       1167 MHz
CPU socket(s):       1
Core(s) per socket:  2
Thread(s) per core:  2
NUMA cell(s):        1
Memory size:         8058840 KiB

Display Virtual CPU information

To display the virtual CPU information, run:

$ virsh vcpuinfo <domain-id or domain-name or domain-uuid>

Example:

$ virsh vcpuinfo centos8-uefi
VCPU: 0
CPU: 3
State: running
CPU time: 5.6s
CPU Affinity: yyyy

VCPU: 1
CPU: 1
State: running
CPU time: 0.0s
CPU Affinity: yyyy

Find IP address of Virtual machines

Finding the IP address of a virtual machine is not a big deal. If you have console access to the virtual machine, you can easily find its IP address using “ip” command. However, it is also possible to identify a KVM VM’s IP address without having to access its console. The following guide explains how to find the IP address of a KVM virtual machine.

Delete Virtual machines

If you don’t want a VM anymore, simply delete it like below:

$ virsh destroy centos8-uefi
$ virsh undefine centos8-uefi

The first command will forcibly stop the VM if it is already running. And the second command will undefine and delete it completely.

You can further use following options to delete the storage volumes and snapshots as well.

--managed-save remove domain managed state file
--storage remove associated storage volumes (comma separated list of targets or source paths) (see domblklist)
--remove-all-storage remove all associated storage volumes (use with caution)
--delete-storage-volume-snapshots delete snapshots associated with volume(s)
--wipe-storage wipe data on the removed volumes
--snapshots-metadata remove all domain snapshot metadata (vm must be inactive)

Manage Virtual networks

List virtual networks

To list of available virtual networks, run:

$ virsh net-list 
 Name      State    Autostart   Persistent
--------------------------------------------
 default   active   yes         yes

As you can see, I have only one virtual network which is the default one.

Display virtual network details

To view the details of a virtual network, run:

$ virsh net-dumpxml default

Replace “default” with your network name in the above command.

Sample output:

<network connections="1">
  <name>default</name>
  <uuid>ce25d978-e455-47a6-b545-51d01bcb9e6f</uuid>
  <forward mode="nat">
    <nat>
      <port start="1024" end='65535'/>
    </nat>
  </forward>
  <bridge name="virbr0" stp='on' delay='0'/>
  <mac address="52:54:00:ee:35:49"/>
  <ip address="192.168.122.1" netmask='255.255.255.0'>
    <dhcp>
      <range start="192.168.122.2" end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>
Start virtual networks

To start an inactive network, run:

$ virsh net-start <Name-Of-Inactive-Network>

To auto-start a network:

$ virsh net-autostart <network-name>
Create virtual networks XML dump

To create the XML configuration file of an existing virtual network, run:

$ virsh net-dumpxml default > default.xml

The above command will create XML config of the “default” network and save it in a file named “default.xml” in the current directory.

You can view the XML file using cat command:

$ cat default.xml 
<network connections="1">
  <name>default</name>
  <uuid>ce25d978-e455-47a6-b545-51d01bcb9e6f</uuid>
  <forward mode="nat">
    <nat>
      <port start="1024" end='65535'/>
    </nat>
  </forward>
  <bridge name="virbr0" stp='on' delay='0'/>
  <mac address="52:54:00:ee:35:49"/>
  <ip address="192.168.122.1" netmask='255.255.255.0'>
    <dhcp>
      <range start="192.168.122.2" end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>
Create new virtual networks from XML file

To create a new virtual network using an existing XML file and start it immediately, run:

$ virsh net-create <Name-of-XMLfile>

If you want to create a network from XML file but don’t want to start it automtacially, run:

$ virsh net-define <Name-of-XMLfile>
Deactivate virtual networks

To deactivate an active network, run:

$ virsh net-destroy <network-name>
Delete virtual networks

To delete a virtual network, deactivate it frist as shown above and then run:

$ virsh net-undefine <Name-Of-Inactive-Network>

Virsh has a lot of commands and options. Learning to use Virsh command line throughly is just enough to setup a complete Virtual environment in Linux. You don’t actualy need GUI applications.

For more details, refer virsh man pages.

$ man virsh

Manage KVM guests graphically

Remembering all virsh commands is nearly impossible and also unnecessary. If you find it hard to perform all Kvm management tasks from command line, you can try graphical KVM management tools such as Virt-manager and Cockpit.

Hope this helps.

Featured image by Elias Sch. from Pixabay.

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